1. Field of the Invention
This invention relates to a rotary shaft seal for the cutter portion of a drill bit used to bore wells such as petroleum and geothermal wells in the earth.
2. Description of the Prior Art
Systems for providing a seal between the rotary cone cutter and bearing pin of a drill bit include O-ring configurations such as disclosed in the specification of U.S. Pat. No. 3,339,928 and metal face seals as described in the specifications of U.S. Pat. Nos. 3,761,145, 4,176,848 and 4,516,641.
There is growing demand for drill bits used in boring petroleum, geothermal and other wells that can operate under the high temperatures and pressures encountered when drilling through hard rock formations at great depth. For this reason, the development of wear- and heat-resistant sealing means for the rotary cutter portion of such drill bits has been eagerly awaited. An O-ring made of heat-resistant resilient rubber may be employed as such sealing means and provides a good seal by virtue of the relative motion between the O-ring and the cutter or between the O-ring and the bearing portion. However, since the O-ring continuously sustains the repeated impact that accompanies such relative motion while also being subjected to high temperatures, deterioration of the resilient rubber constituting the O-ring is accelerated and, as a result, rapid destruction of the seal at the rotating portion of the drill is unavoidable.
In an effort to solve the problem of the O-ring seal caused by such deterioration of the resilient rubber, a sealing mechanism capable of withstanding the conical movement of the cutter has been fabricated in which a heat- and wear-resistant metal seal of high hardness is used at the rotary seal portion and is supported by a seal made of a heat-resistant resilient rubber. This latter mechanism is the metal face seal referred to above. The metal face seal arrangement is composed of a comparatively large number of component parts that, when assembled, result in a seal structure of some complexity. In addition, because of the dragging or scoring that occurs between the hard metal components and due to the combination of the hard metal material with the soft natural rubber, an excellent sealing property cannot be maintained over a very long period of time.